1. Field of the Invention
The present invention is directed to a materials inspection system using x-ray imaging, such as a baggage inspection system wherein articles being inspected are moved on a conveyor system through an x-ray beam. The system disclosed herein is particular suited for identifying organic material, such as drugs or explosives, in the inspected articles.
2. Description of Prior Art
Baggage inspection systems are known which generally include a conveyor for moving the articles to be inspected through a beam of x-rays. The x-ray beam is emitted on one side of the articles from an x-ray source, and a radiation detector is disposed on the opposite of the moving articles. The radiation detector is formed by a row of individual detector elements. A signal processing circuit is connected to the outputs of each of the individual detector elements, from which a visual reproduction of the contents of the inspected articles can be obtained and displayed.
It is known in medical radiology to use x-rays of different energies to conduct a radiological examination. The radiation energies are selected based on the mass attenuation coefficient and ordering number of of the chemical elements which are expected to be present in the examination subject.
By comparing at least two congruent x-ray images at different energy levels, it is possible, for example, to distinguish soft tissue (elements having a lower ordering number) from bones (elements having a higher ordering number).